Linear capacitively coupled touch sensor and method

Abstract

A system includes a capacitively-coupled touch sensor having a conductive first layer and a conductive second layer on a first insulative layer. The width of the second layer varies along an axis of the first layer. A first excitation signal is applied to one of the first and second layers and is capacitively coupled through a touch element to the other layer, producing a first signal that produces a second signal which is digitized. Digitized peak values of the second signal are processed to compute a value for a touch element location. A conductive third layer can be placed on the opposite side of the first layer has width varying oppositely to the second layer. The first excitation signal is applied to the second layer and a non-overlapping second excitation signal is applied to the third layer. The resulting digitized peak values are processed to cancel errors due to variations.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to capacitively-coupled touch sensors, and more particularly to capacitively-coupled “slider” sensors which respond to touch by generating a linear output signal relative to the position of a user's finger as it slides along the surface of a touch sensor. The invention relates still more particularly to such a linear capacitively-coupled touch sensor that is essentially independent of variations in finger pressure and various other “environmental” variables.[0002]Capacitively-coupled touch sensors are well understood, and are becoming widely used in modern electronics to replace mechanical switches as input devices for command and control functions. In many common applications, an individual touch sensor performs a single function such as turning a lamp on or off. In previous designs, multiple individual capacitively-coupled touch sensors with digital outputs have been positioned side-by-side and utilized in co...

AI Technical Summary

Benefits of technology

The invention provides a capacitively-coupled touch sensor and method that can act as a linear control switch, allowing for precise sensing of user finger touch without the need for separate sensors or complicated signal interpretation. This results in an easier and more cost-effective solution.

Problems solved by technology

Unfortunately, the use of multiple individual capacitively-coupled touch sensors and interpolation techniques as indicated above to provide pseudo-linear functionality may be too complex and costly for use in a modern laptop computer or other electronic device in which available space for switches and the like is at a premium.

Unfortunately, the capacitive coupling is significantly affected by the above-mentioned variations in the touch pressure of Finger 19 (and also by variations in some other “environmental” parameters, such as humidity and user skin conductivity).

The effect of variation of the finger pressure on the amount of the capacitive coupling between outer plate 3 and inner plate 2 ordinarily would be undesirable because such variation causes the determination of the present finger touch location to be inaccurate.

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